To most plant manager's, maintenance supervisor's, and purchasing agents the purchase price is the deciding factor when buying lubricants. While the initial cost of synthetic lubricants are often five-times the cost that of petroleum-based lubricants, is certainly a factor, but should not be the only factor. The type and age of equipment, severity of service, final product, operating temperatures, geographical location of your plant should be used to help determine on whether to use synthetic or petroleum-based lubricants.

The basic difference between petroleum-based and synthetic lubricants is the base fluid. Petroleum-base lubricants are extracted from natural crude oil, and must be refined, desalted, dewaxed, and distilled from crude feedstock. These base fluids are made up of a great variety of naturally occurring hydrocarbons arranged in many molecular configurations. There are families of hydrocarbons that are segregated throughout the refining of crude oil.

Synthetic lubricants, which have been in existence for more than half of the roughly 100 years during which time petroleum-based lubricants have been used by major industrial plants, are developed in research laboratories. When something is synthetic, it has been created through the combination of separate parts into a whole (synthesized). As a chemical term, synthetic refers to a compound formed through a chemical reaction that did not occur naturally. The entire molecular structure of a synthetic lubricant is determined by tailored, tightly controlled chemical reactions; hence, the higher cost of synthetic lubricants.

Different synthetic lubricants are made from different base fluids. Table 1 below compares the properties of four (4) different base stocks. Here are some facts about three (3) common synthetic base fluids.

ORGANIC ESTERS are made up of dibasic acid esters or polyol esters. Both can be used at temperatures exceeding 400°F. Dibasic acids are particularly effective as base fluids for compressor lubricants, while polyol esters are used in lubricants for industrial chains and gas turbines.

PHOSPHATE ESTERS serve as the base fluid for many lubricants used where there is a risk of fire.

SYNTHETIC HYDROCARBON FLUIDS (SHF) are manufactured by combining hydrocarbons of butylene or ethylene to create a polyalphaolefin (PAO) base fluid. SHF bases are used in numerous applications because of their superior temperature range and lubricating properties.

There is no question that synthetic lubricants have demonstrated advantages over petroleum-based products in several areas.

· Extended Oil Drains. Due to the thermal and oxidative stability of synthetic lubricants, oil drain intervals can be greatly extended.

· Energy Savings. Synthetic lubricants' viscosity index, friction properties, and heat transfer characteristics result in measurably less horsepower required to drive equipment in both hot and cold environments.

· Fire Resistance. Because the high flash point of synthetic lubricants reduces the risk of fire, some insurance companies charge lower premiums for plants using synthetic lubricants.

· Fewer Deposits. Because of their oxidative stability at high temperatures, synthetics leave very few deposits. The resulting decrease in equipment wear often results in fewer repairs and down time.

No matter what size the plant, there are several applications for which synthetic lubricants are highly recommended.

Air Compressor Duty. Nearly every air compressor manufacturer recommends draining a synthetic lubricant after 8,000 hours, as opposed to 1,000 hours with a petroleum-based lubricant. Aside from drain intervals, air compressors require a lubricant which provides excellent oxidation resistance, because they compress air at very high temperatures, often 250°F and higher.

Extreme Temperature Duty. Synthetic lubricants have superior viscosity-to-temperature characteristics that make them especially suitable for use in refrigerators, ovens, or plants in hot or cold climates.

Continuous Duty. When equipment shutdowns for oil changes absolutely must be minimized, synthetics are the obvious choice because they need to be changed so infrequently. Plants that run an assembly line-type process -- meaning if one piece of equipment is down, all production stops -- may find the use of synthetic lubricants most economical.

Here are several applications where petroleum-based lubricants shine.

High Consumption Applications. The classic example is equipment that has accumulated very many operating hours and become worn, resulting in increased lubricant consumption. Because of their low initial cost, petroleum-based lubricants are the much more economical option in high-consumption applications.

Once-Through Applications. Petroleum-based lubricants are always the economical option in equipment that has no reservoir -- applications in which oil sprays into the cylinder, lubricates the piston, and then blows down line as in gas compressors.

Product Contamination Applications. In a natural gas liquid processing plant, neither synthetic nor petroleum-based lubricants can completely escape contamination by the final product when it enters the crankcase.

The resulting need for frequent oil changes points to petroleum-based lubricants because of their lesser unit cost.

Very Dirty or Dusty Environments. Unlike automotive motor oils that are designed to suspend dirt and deposits, industrial oils are designed to clean, cool, and seal the equipment they are lubricating. Neither synthetic nor petroleum-based lubricants are designed to suspend dirt and dust blown into the equipment from the exterior. Therefore, petroleum-based lubricants are the cost-effective choice for equipment operated in extremely dirty or dusty environments.

Oil analysis should be a key tool in any preventive maintenance program, whether the plan incorporates synthetic or petroleum-based lubricants. There are two main components of oil analysis; spectrometric analysis and physical tests.

Spectrometric analysis is used to measure the levels of metals in the oil, and aids in determining equipment condition. With this information, plant maintenance supervisors can plan downtime for inspection and/or repairs.

Equipment interior wear conditions and resulting oil contamination should be monitored, regardless of the lubricant used. It's also important to use spectrometric analysis to check the condition of all equipment scheduled to be switched to synthetic lubricants before making the switch.

Physical Tests

Results of physical tests help determine how long oil can remain in equipment.

Viscosity. The internal resistance to flow of a lubricant is perhaps the key determining factor in whether an oil needs to be changed.

Particle Count. A high particle count when measuring solids in oil, such as fuel soot and sludge, often indicates that a new oil filter is needed.

Nitration. An indication of contaminants from accumulation of combustion byproducts, such as abnormal blow-by, is also a signal for a change.

Consider the lubrication of two identical pieces of equipment in a plastic extrusion plant over an 8,000-hour period. Each machine has a 20-gallon sump. (See Table 2 below).

Machine A is lubricated with 20 gallons of synthetic lubricant, which is drained and replaced at a recommended interval of 8,000 hours. Lubricant cost is $25.00 per gallon for a total 8,000-hour expenditure of $500.00 (20 gallons x $25.00 x 1 oil change).

Machine B is lubricated with 20 gallons of petroleum-based lubricant, which is drained and replaced at factory-recommended 1,000-hours intervals. The cost of the petroleum-based lubricant is $5.00 per gallon. The total 8,000-hour expenditure is $800.00 (20 gallons x $5.00 per gallon x 8 oil changes).

Now consider the cost for labor and oil disposal associated with both machines. The oil in Machine A is changed once in an 8,000-hour time span, If the oil change procedure requires one man-hour of labor, the plant pays, say $50.00 for the hour of labor, and $10.00 for disposal of the 20 gallons of oil (20 gallons x disposal cost of $0.50 per gallon).

The oil in Machine B is changed every 1,000 hours, or 8 times within the 8,000 hours that Machine A is running on synthetic lubricant. If each 8 oil changes requires an hour's labor, the cost is $400.00 (8-hours x $50.00 per hour). Disposal of the 160 gallons of oil resulting from the 8 drains costs $80.00 (160 gallons x $0.50 per gallon disposal cost). In addition, the plant may have lost revenue due to down time during oil change -- 8 times as much for Machine B as for Machine A.

Plant size plays an important role. For a single machine such as discussed in the example, it may be very difficult to justify the up-front investment and carrying costs of up to $1,375.00 (55 gallons x $25.00 per gallon) for a 55 gallon drum of synthetic lubricant alone. Even at 8,000 hours per oil change and three-shift operation, the first 20 gallons would take nearly a year to be consumed. Compare that with a total cost of $1,280.00 (including labor and disposal) to lubricate the piece of equipment for 8,000 hours with petroleum-based lubricant.

For a larger number of machines, the situation reverses. The savings from using synthetic lubricant for 100 machines far outweigh the extra lubricant cost.

This breakdown of costs for maintaining two identical items of equipment in a plastics extrusion plant illustrates savings from using a synthetic lubricant. However, the considerable up-front cost of synthetic (as much as $1,375.00 for a 55 gallon drum) means that plant size (number of machines) also play a role in choosing the right lubricant.

The important points to remember is that more factors than just purchase price determine the net cost of using a particular lubricant. Type of application and plant size are the primary factors in determining whether a synthetic or petroleum-based lubricant is most cost-effective.